1. Field of the Invention
The present invention relates to a so-called positive lead type zoom lens in which a first lens unit has a positive refractive power, and an optical apparatus having the same.
2. Description of the Related Art
In focusing in a positive lead type zoom lens by moving out the entire first lens unit, an aberrational correction may become insufficient at a close end side on which a focus moving amount becomes larger because a single lens unit provides in-focusing and aberrational corrections. Accordingly, each of Japanese Patent Laid-Open Nos. 07-43611 and 2000-284174 divides, in order from the magnification conjugate side, a F11 sub-unit having a positive refractive power, and a F12 sub-unit having a positive refractive power, and moves the F12 sub-unit to the magnification conjugate side for focusing. The prior art reduce deteriorations of the imaging performance associated with focusing from the long object distance to the close end position by adjusting the power of each sub-unit.
However, the methods proposed by Japanese Patent Laid-Open Nos. 07-43611 and 2000-284174 are insufficient in restraining the aberrational variations since the height of an off-axis principal ray in the F12 sub-unit significantly changes during focusing from the distant position to the close end position.
In addition, the ghost has recently been problematic which is caused when light reflected on the reduction conjugate plane by an element is reflected on an arbitrary surface in the lens and again reaches the reduction conjugate plane. In that context, an element having a high surface refractive index has been increasingly used as an element for the reduction conjugate side such as a Liquid crystal on Silicon® (LCOS) for a reflection type projector and a CCD or a CMOS for a digital camera. Conventionally, this ghost is an issue in the first lens unit of the positive lead zoom lens.